The present invention relates to a method of reproduction in a disk playing apparatus.
A small digital audio disk having a diameter of about 12 cm and called a "compact" disk is well known as an information storage medium on which a digital signal is recorded.
Recently, a disk (which is hereinafter referred to as a "composite" disk), which has the same size as a compact audio disk and on which a PCM (pulse code modulation) signal and a frequency-modulated video signal are recorded in a mutually superposed state, has been developed. As shown in FIG. 1, the composite disk has a first region 1a, here termed a CD region, which is an inner region and in which an audio signal subjected to PC is recorded, and a second region 1b, called a video region, which is an outer region and in which a frequency-modulated video signal and an audio signal subjected to PCM are recorded in a superposed state.
Since the video signal contains components whose frequency is higher than that of the audio signal, the frequency spectrum of the signals recorded in the video region 1b is as shown in FIG. 2, in which A denotes the PCM modulated audio signal and B denotes the frequency-modulated video signal. Due to the difference in signal frequency content between the region A and B, the rotational speed of the composite disk must be made higher at the time of recording of the video signal in the video region 1b than at the time of recording of the audio signal in the CD region 1a, and hence the rotational speed of the composite disk must also be made higher during reproduction of the video signal from the video region 1b than during reproduction of the audio signal from the CD region 1a. (See FIG. 3.) The speed of the composite disk for the recording and reproduction of the audio signal in and from the CD region 1a is several hundred rpm, while that of the composite disk for the recording and reproduction of the video signal in and from the video region 1b is typically more than two thousand rpm for the innermost portion of the region and more than one thousand rpm for the outermost portion thereof.
In a disk player for such a compact or composite disk, the information detecting point of a pickup follows the recording track of the disk to read recorded information therefrom. However, if external vibration acts on the player, the information detecting point of the pickup can be caused to jump recording tracks, resulting in making the reproduction of the disk unstable. Compact disk players have heretofore been adapted for use in motor vehicles, and it is desired to do the same for a composite disk player because the size of the composite disk reproducer is as small as that of the compact disk player. However, since a moving motor vehicle always vibrates to some extent, countermeasures need to be taken to prevent the information detecting point of the pickup of the composite disk reproducer from jumping the recording track of the composite disk due to such vibration.